Field of the Invention
The present invention is directed to an exhaust treatment apparatus for use in the exhaust system of an internal combustion engine and, in particular, to a catalytic converter having means for varying the cross section of the catalyst substrate to reduce the time to converter light-off.
Typical automotive vehicle exhaust systems, and an increasing number of non-automotive applications incorporating internal combustion engines, utilize catalytic converters in the exhaust system for reducing the quantity of regulated constituents emitted to the atmosphere. Common configurations consist of ceramic or metal foil catalyst coated monoliths enclosed in a rigid, stainless steel canister which is interposed within the exhaust system in an underbody location.
As a precondition to the efficient conversion of gas emitted from the engine, the catalyst must reach a minimum operating temperature generally referred to as the light-off temperature. As emission regulation has become increasingly stringent, the reduction of untreated exhaust gas emitted prior to light-off of the converter has become increasingly important.
One method of achieving lower light-off times is through the use of a small "pup" converter which is mounted in close relation to the engine, and is of a relatively small volume when compared to most typical converters. The location and size of the pup converter allows for a relatively rapid catalyst light-off but may adversely affect exhaust system backpressure. Part-time use of the pup converter is generally contemplated with a bypass to direct the exhaust gas to a larger, underbody converter once the larger converter reaches a suitable operating temperature.